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by: Mr. Nathan Borer


Mr. Nathan Borer
GPA 3.6


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Class Notes
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This 5 page Class Notes was uploaded by Mr. Nathan Borer on Sunday September 27, 2015. The Class Notes belongs to CPR E 458 at Iowa State University taught by Govindarasu in Fall. Since its upload, it has received 47 views. For similar materials see /class/214525/cpr-e-458-iowa-state-university in Computer Engineering at Iowa State University.

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Date Created: 09/27/15
Michael Bullis CprE 458 Term Project Fall 2011 Android DVFS Do you wish you could get more battery life out of your smartphone With the increasing processing power in embedded mobile devices battery life is becoming an important issue The number of peripherals has increased in phones as well so reducing the amount of energy used in each component can help increase the battery life Adjusting the CPU frequency or voltage is a way of reducing the amount of energy used by the processor Although Android is not a real time operating system by itself some of the real time topics discussed in class can be applied to energy management in an Android devices Specifically we can use the concept of dynamic frequency voltage scaling to help improve the battery life of our smartphones We have learned that Energy used is proportional to operating time the operating frequency and the operating voltage E oc t X f X V2Although we Frequency Voltagemv cannot directly examine the amount of energy used by our physical 1300000 1400 1200000 1350 device we can indirectly measure energy usage by looking at the 1000000 1250 800000 1200 battery level percentage that Is offered through the Andr0d API 600000 1150 d h f Id I b h 400000 1050 Base on t Is In ormatIon we wou expect to use ess attery w en 200000 950 100000 950 we are operating at a lower frequencyOften frequency and voltage Figural scaling are done in conjunction This can be examining quot 39 39st m m mquot mf 1 f voltagetable The results are shown in Figure 1above Android is backed by a Linux operating system Most original equipment manufacturers OEMs place restrictions and bloatware on top of the AndroidLinuxoperating system This usually restricts root or superuser access Root access is needed to modify files needed to change the operating frequency of our processor The file that we will be using to scale the processor frequency is quot 39 39st m m punp f 1 quot set speedAscreenshot ofthe file permission is shown below in Figure 2 The figure shows that that scalingsetspeed file was created by a process running with the root UID Figu re 2 For this project I chose to use my own personal Samsung Mesmerize This device contains an ARM version 7 revision 2 processor My first plan of action was to obtain root access to an Android device In order to obtain root access used the z4root application that I downloaded from the internet I could have gained root access by manually running a shell script with a terminal emulator but I chose to use the premade application to save time Once I obtained root access I was able to flash a custom ROM running Android version 235 Gingerbread The ROM I chose to use was the popular Cyanogenmod 710 The Cyanogen ROM allows the user to choose the CPU governor that the underlying Linux operating system uses Using the Cyanogen interface the user can specify a minimum and maximum processor frequency There are five different types of CPU governors that one can choose from These governors are Userspace Ondemand Conservative Performance and Powersaving Governors Performance This governor statically sets the processor speed to the maximum frequency specified It will be the most responsive but will also drain the battery the fastest Powersaving This governor statically sets the processor speed to the minimum frequency specified It will be the least responsive but will also result in the longest battery life of all the governors mentioned Ondemand This governor instantaneously jumps between the minimum and maximum frequencies as the workload changes Conservative This governor gradually increases the processor speed between the minimum and maximum frequencies as the workload changes If the workload is small and the current frequency is at the maximum frequency then the processor will slowly start decreasing its speed until it reaches the minimum frequency The processor will remain at this frequency until the workload increases It will then start to gradually increase its speed until it reaches the maximum frequency Userspace This governor allows for processes and applications running with the root user id to dynamically alter the processor speed This is the governor that I used to implement my own custom governing algorithm Governor Benchmarks I predicted the performance of these governors prior based on their descriptions I predicted that the performance governor would be able to outperform all of the other governors because its operating frequency is the highest Consequently Ithought that the powersaving governor would have the worst performance The ondemand governor should be a close second to the performance because it can instantaneously scale the operating frequency from the minimum to maximum frequency as needed This governor will offer limited energy conservation because any relatively demanding workload will need more than the minimum clock frequency to be able to complete its tasks in a reasonable amount of time I predicted that the conservative governor would slightly trail the ondemand governor in performance while offering slightly better battery savings After establishing these predictions I decided to run the popular PassMark Android benchmarking application to put my hypotheses to the test The results can be found in the attached TestResultsxlsx file The chart indicates performance was greatly decreased with the powersaving governor The user interface was practically unresponsive at times using this governor When I was using the performance governor I noticed a very snappy response time with almost no lag These results seem to support my predictions about performance but offer no insight as to the amount of energy used To gain some information about relative battery used I chose to benchmark these governors by compiling regular expression strings in Java Compiling regex expressions can be computation intensive if the expressions are complex enough Iran this test


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